1. Field of the Invention
This invention relates generally to the cardiac rhythm monitoring. More particularly, the invention relates to detection, classification, and display of ectopic beat patterns by their statistical indices and time domain signatures.
2. Description of the Related Art
Physicians typically detect ectopic beats by visually analyzing electrocardiograms (ECGs). To detect the beats, the physician analyzes changes in waveform morphology from the ECG tracings. The ECG tracings provide the physician with a large amount of data to examine while looking for the ectopic beats. In addition, the examination generally requires a patient to visit a physician""s office and be hooked up to an ECG recording device. Although this procedure identifies ectopic beats during the office visit, the procedure does not reveal the history of ectopic beats that would help to better assess the patient""s overall well being. Alternatively, the patient may transmit ECG data to the physician using a telephone line. Unfortunately, telephonic transmission of heart rate rhythms typically does not include all of the data from the ECG recording due to limitations on telephonic transmission of the data. Therefore, this method is not as accurate as an office visit.
Due to the large amounts of data needed to record waveforms for a physician to observe morphology related ectopic beats, the ECG""s used are usually not from implantable devices which typically have limited data memory. Therefore, implantable devices can only provide short snapshots of the morphology data needed to detect ectopic beats.
Hence, there is a need to provide an implantable device for monitoring ectopic beats long term for assessing patient well being and providing the physician with useful trending data for diagnosing and treating a patient.
The present invention provides a method of detecting ectopic beats requiring less memory than a full ECG tracing. The reduced memory requirement permits the methods use in conjunction with implantable medical devices such as pacemakers.
By limiting analysis of ectopic rhythms to strictly interval sequences of interval profiles, a longer record of the patient""s ectopic heart activity based solely on the intervals themselves can be stored. One of the benefits of using the intervals is that it requires less memory. Another benefit is that the characterization methods are different and because it requires less memory to get representation of the ectopic beats an implantable device is possible.
A normal R to R interval is established by looking at the median of R to R intervals for a period of time. A threshold can then be established as a percentage above and below the median of the R to R interval. These upper and lower thresholds are used to determine whether or not an event is ectopic.
After having determined an event is ectopic, a microprocessor assigns a value of normal (n), short (s), or long (l) to the R to R interval and stores the sequence of determinations (i.e., n, n, n, s, l, s, l) that characterizes the event sequence. The R to R interval""s values (i.e., n, s or l) form patterns. The stored patterns are used as a dictionary for classifying the ectopic event types. The event types are identified by the microprocessors which then counts and reports events over an extended period of time. The microprocessor may also be programmed to change pacing therapy.
A transmitter connected to the microprocessor can then report the data collected by telemetry to a receiver. The receiver can then transfer the data to a device which converts the data into graphical form for presentation to a physician for analysis.